Semiconductor solar cells generally produce a light-generated output voltage that is roughly proportional to the equivalent bandgap of the material systems used to fabricate the solar cell. Under illumination, this output voltage typically ranges from less than one volt for low-efficiency single junction cells to nearly three volts for high-efficiency multi junction cells. In order to deliver a larger voltage to a load, cells are typically connected in series, whereupon the total output voltage becomes equal to the voltage of a single cell multiplied by the number of series-connected cells. The series connection of cells generally requires that the cells each operate at an identical current. With precise cell matching and uniform illumination over the large-area panel, this condition is often not restrictive. However, in situations where the photo-current of a single cell is reduced relative to the other cells in the string, all cells become limited to that reduced photo-current. This reduction in photo-current may result from physical damage, partial shading of the incident light, systematic variations in cell performance, or a localized temperature change in a particular cell. In extreme cases, the current reduction may lead to large reverse biases forming across the limiting cell, which in turn may lead to localized overheating and permanent physical damage. In order to prevent this particular failure mechanism, the use of discrete bypass diodes wired across individual cells or groups of cells in series is often employed. Bypass diodes help prevent the formation of large reverse biases and enable the non-limiting cells to operate closer to their optimal power output.
In conventional solar-panel designs the individual cells are manufactured from large-area semiconductor substrates (or large pieces thereof), typically 8 cm×8 cm pieces or larger. For applications requiring high-voltage operation, the series connection of many of these large-area cells results in an array string that occupies a much larger physical area (i.e., roughly equivalent to the sum of the areas of the individual cells). Because of the large area required, the string becomes more susceptible to partial shading that may significantly reduce the total output power of panel (as discussed above). Similarly, because the total power of the panel is generally proportional to the total area, large-area arrays are particularly susceptible to physical damage. In the worst case, physical damage to a single cell may shut down the entire series-connected string. Additionally, in situations where large temperature gradients exist over areas on the order of the size of the string (in solar-powered aircraft, for example) the performance of the entire string may become limited by the cells producing the least current. Lastly, because the entire semiconductor substrate is typically used in the fabrication of conventional solar panels, the addition of bypass diodes and other circuitry is generally performed with external discrete components. This increases the complexity and cost of the final panel assembly, as well as the total panel weight, any or all of which may represent critical design parameters, depending on the application.